The present invention relates to novel insecticidal gel formulations for the controlled and sustained release of insecticidal active compounds by means of a heat source. These novel gel formulations are characterized in that they comprise at least one type of insecticide and at least one vaporization-controlling substance (vaporization modifier), in combination with a solid suitable as a gel former.
The present invention is based on known gel formulations as described in EP 0 693 254, where insecticidally active compounds with novel, alternative solvents in combination with perfumes, colorants and auxiliaries are to display an optimum effect without decomposition for a relatively long period of time.
This novel active compound formulation is to be used in deep-drawn or cast containers made of polymer or metal, these containers being open or closed by means of suitable fabrics, films made of polymer, for example polypropylene film, or metal, which are permeable to the volatile components, as described in EP 0 693 254. These deep-drawn containers can be used in an electrical heating device for killing insects, for example mosquitoes.
In the case where mosquitoes are killed using an electrical heating device, a so-called tablet vaporizer, it is generally known that specifically selected substances, such as cellulose board and cotton board, asbestos, ceramics and/or porous synthetic resins are impregnated with pyrethroid insecticides to obtain insecticide tablets, the insecticides being volatilized by the action of the mosquito killing heating device, which generates a temperature of 120-190xc2x0 C.
A considerable disadvantage of these tablet vaporizers is the unfavourable ratio between energy input and active compound to be vaporized, since the proportion of active compound relative to the auxiliaries is to be considered as low. Furthermore, the high working temperature of these tablet vaporizers means that only few active compounds are suitable for this purpose in the first place, and that, moreover, these active compounds are released over the predetermined period of action in a non-uniform manner, for system reasons. The period of action of these vaporizer tablets is limited to a maximum of 12 hours. Finally, the unfavourable ratio of active compound/active compound carrier requires a substantial, constantly available stock of vaporizer tablets, which means that large amounts of material are necessary as carriers and packaging material.
The devices which are already widely used for domestic purposes, in which a solution of an insecticidally active compound is vaporized by means of a heated wick (GB 2 153 227), where the active compound is dissolved in a kerosene mixture of saturated aliphatic hydrocarbons which is vaporized electrically by means of the wick, also have considerable disadvantages.
Apart from the fact that these vapour-producing systems also operate at temperatures of between 120 and 190xc2x0 C., they require a specific distribution system (wick) and considerable amounts of solvents. When the product is used, the superproportional amount of solvent relative to the active compound results in a high concentration of solvents or adjuvants in the room, which, in turn, leads to dirtying of walls and objects in the vicinity of these devices, which has frequently been observed by customers and given cause for complaint.
Other disadvantages of these formulations are the high volume of the solvent containers and the risk of the solvent leaking, which means that there are substantial problems during transport and hazards in use.
Furthermore, EP 0 693 254 mentions gel formulations which have the disadvantage that they persist for a long time indoors and that they additionally consist of very expensive components.
The novel insecticide-comprising gel formulations according to the invention include mixtures which comprise at least one type of a pyrethroid insecticide, a vaporization-controlling substance and an inorganic solid suitable as a gel former.
Suitable active compounds which can be used are the active compounds mentioned in EP 0 693 254.
Particularly suitable here are formulations with the active compound transfluthrin (Bayothrin(copyright), 2,3,5,6-tetrafluorobenzyl (+)-1R-trans-2,2-dimethyl-3-(2,2-dichlorovinyl)cyclopropanecarboxylate) having a reduced active compound content and in combination with novel vaporization-controlling substances, also referred to as vaporization modifiers, which have a strongly reduced risk potential during processing and which are furthermore rapidly degradable indoors.
Preferred novel vaporization modifiers are medicinal white oils CAS No. 8042-47-5 (BP Enerpar M002(copyright)) and high-pressure hydrogenated mineral oils CAS No. 8042-47-5 (Enerpar M1930(copyright)).
Particular preference is given to naturally regrowing raw materials such as rapeseed oil, rapeseed oil methyl ester and colourless to slightly yellowish Guerbet alcohol of liquid/solid consistency having a very weak intrinsic odour, CAS No.: 67 187-86-0 (Guerbitol 32/36(copyright)), colourless to slightly yellowish Guerbet aalcohol of liquid consistency having very weak intrinsic odour=2-hexyldecan-1-ol, CAS No.: 36311-34-9 (Guerbitol 16(copyright)).
Particular preference is given to colourless to slightly yellowish Guerbet alcohol of liquid consistency=2-hexyldecan-1-ol, CAS No.: 36311-34-9 (Guerbitol 16(copyright)).
The formulations generally comprise between 1.0 and 95% by weight of insecticidally active compound, preferably between 5.0 and 80%, in particular from 20 to 50% by weight.
The formulations furthermore generally comprise between 10 and 90% by weight of vaporization modifiers, preferably between 40 and 80%, and generally between 1 and 12% of gel former, preferably between 6 and 10%.
The ratio of active compound/vaporization modifier in the insecticide-comprising gel formulations according to the invention is between 9 and 0.1; preferably between 2.0 and 0.2.
It is furthermore possible to add organic or inorganic auxiliaries, stabilizers, perfumes and colorants, as described in EP 0 693 254, inter alia, to these mixtures.
The formulations must have an optimum storage stability over a long period of time.
The gel formulations according to the invention are prepared by first stirring at room temperature in a suitable mixing apparatus (planetary paddle mixer) the active compound with the vaporization modifier and stabilizer and, if appropriate, additional solvents, to give a clear solution. Then, the gel former is added under reduced pressure, and the mixture is stirred vigorously until a homogeneous gel is formed. Before the gel former is mixed in to give the final gel product, perfume oils and colorants can optionally be added to the existing clear solution with stirring until the mixture is completely homogeneous.
For use, the film container with the coloured gel is inserted into a heating device whose front is transparent or fitted with an inspection opening.
During the use of the heating device, the content of the film container, which is not visible through a colour marking on the container itself or on the heating device, dries out.
Only the empty film container is still visible through the transparent front of the heating device or through the inspection opening.
A further variant for visual identification of the end point using added colorants may also take the form of a change in colour when the active compounds and, if appropriate, the solvent have vaporized.
The present invention is to be illustrated by the present examples: